This invention relates to multi-stage presses in which generally large workpieces, such as vehicle body parts, are deformed in consecutive press stages while the articles are conveyed from stage to stage and are supported by gripper assemblies. The latter are held on a gripper rail which is formed of a plurality of end-to-end arranged rail portions. Usually, in each press stage there is situated one rail portion whose length generally corresponds to that of the press stage. In case of tool replacement in any press stage, the work tool set of that stage, together with the associated gripper rail portion (which carries the gripper rail assemblies) is rolled out of the press on a table in a direction transversely to the press length. Subsequently, the new tool set is, with the associated gripper rail portion, shifted back into the press stage. For an automatic tool replacement the gripper rail portions associated with the press stage where tool replacement is to be performed, are automatically disconnected from the gripper rail string.
Multi-stage presses, particularly in the zone of supporting columns, have at least one "empty stage" that is, a zone in the sequence of the stages where no work on the workpieces is performed. The workpieces, however, dwell in the empty stages on their way to or from a press stage and therefore have to be positioned by gripper assemblies in the same manner as they are positioned in the press stages. Consequently, when work tool replacement is taking place, particularly because a change in the workpiece is contemplated, the gripper assemblies also have to be replaced and this applies equally to the gripper assemblies that serve the empty stages. It therefore follows that, together with the tool assemblies and the gripper assemblies of the work stage, the gripper assemblies of an adjacent empty stage have to be replaced as well.
According to a known solution in a multi-stage press having a single empty stage, a single gripper assembly is shifted from the empty stage to a rail portion of a press stage preparatory to moving out the tool set and the gripper assemblies of the press stage. Such a known arrangement, however, provides only for a sole gripper assembly to be shifted from a gripper rail portion associated with an empty stage to the gripper rail portion associated with an adjacent press stage. It is further noted that in the prior art, the grippers designed to engage one and the same workpiece have been, on any particular side of the workpiece, formed as one-piece slidable constructions.